The inauguration of Thomas Jefferson marked the first time in U.S. history that a major philosophical change in U.S. government took place. The United States nearly doubled in size during Jefferson's presidency by purchasing the Louisiana Territory from France. Lewis and Clark were hired to explore the northern acquisitions, and Zebulon Pike was sent to explore the South and the West. The move west continued. In the mid-1800's, people living in New Spain [Mexico] faced difficult conditions. Eventually, revolutionaries overthrew the Spanish and established a new Mexican republic. People living in Texas, which was part of Mexico, soon rebelled against what they considered to be unfair laws imposed by the Mexican government.

Border disputes along he southern boundary of Texas led to the Mexican War. After a U.S. victory, Mexico agreed to turn over much of its northern lands to the United States. In the 1853 Gadsden Purchase, Mexico sold a strip of land to the United States, finally fixing U.S. continental boundaries. 

By the end of this period of exploration in history, you will be able to do the following:
 In this section you will:
1. Analyze the reasons that Thomas Jefferson wanted the United States to control New Orleans.
2. Describe the purpose of Lewis and Clark's expedition and the conditions of their journey.
3. Describe what life was like on the Oregon Trail.
4. Explain why people used the California and the Santa Fe Trails despite the hardships they faced along the way.
5. Describe how America's belief in manifest destiny affected westward expansion.